Catheter having circular ablation assembly

ABSTRACT

A catheter particularly useful for ablation lesions within a tubular region of or near the heart is provided. The catheter comprises an elongated flexible tubular catheter body having an axis and proximal and distal ends. An ablation assembly is mounted at the distal end of the tubular body. The ablation assembly has a preformed generally circular curve having an outer surface and being generally transverse to the axis of the catheter body. The ablation assembly comprises a flexible tubing having proximal and distal ends that carries a tip electrode at its distal end. An electrode lead wire extends through the catheter body and into the ablation assembly and has a distal end connected to the tip electrode. In use, the distal end of the catheter is inserted into the heart of a patient. At least a portion of the outer circumference of the generally circular curve is contacted with the inner circumference of the tubular region so that the tip electrode is in a first position in contact with tissue along the inner circumference. The tip electrode is used to ablate tissue at the first position. The ablation assembly can then be rotated so that the tip electrode is in a second position in contact with tissue along the inner circumference different from the first position, and the tip electrode is used to ablate tissue at the second position. This procedure can be repeated to form a lesion of the desired length along the inner circumference.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/118,680,filed Apr. 9, 2002, titled CATHETER HAVING CIRCULAR ABLATION ASSEMBLY,now U.S. Pat. No. 6,733,499, issued May 11, 2004, which claims thebenefit of U.S. Provisional Patent Application No. 60/360,431, filedFeb. 28, 2002, the disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

The resent invention relates to an improved ablation catheter that isparticularly useful for ablating in a tubular region of or near theheart.

BACKGROUND OF THE INVENTION

Atrial fibrillation is a common sustained cardiac arrhythmia and a majorcause of stroke. This condition is perpetuated by reentrant waveletspropagating in an abnormal atrial-tissue substrate. Various approacheshave been developed to interrupt wavelets, including surgical orcatheter-mediated atriotomy. A common procedure involves ablating alesion to interrupt the wavelets using one or more electrodes mounted onthe distal end of a generally-straight catheter. This procedure workswell, for example, when ablating a line of block in the atria. However,for tubular regions in or around the heart, this procedure is lesseffective. For example, when the line of block is to be made about acircumference of the tubular region, it is difficult to manipulate andcontrol the distal end of a straight catheter so that it effectivelyablates about the circumference. Accordingly, a need exists for animproved catheter that is particularly useful for such applications.

SUMMARY OF THE INVENTION

The present invention is directed to a catheter having agenerally-circular ablation assembly mounted on its distal end thatcarries a tip electrode. In one embodiment, the catheter comprises anelongated flexible tubular catheter body having an axis and proximal anddistal ends. An ablation assembly is mounted at the distal end of thetubular body. The ablation assembly has a preformed generally circularcurve that is generally transverse to the axis of the catheter bodycomprising a flexible tubing having proximal and distal ends andcarrying a tip electrode at its distal end. An electrode lead wireextends through the catheter body and into the ablation assembly and hasa distal end connected to the tip electrode.

In use, the distal end of the catheter is inserted into the heart of apatient. At least a portion of the outer circumference of the generallycircular curve is contacted with the inner circumference of the tubularregion so that the tip electrode is in a first position in contact withtissue along the inner circumference. The tip electrode is used toablate tissue at the first position. The ablation assembly can then berotated so that the tip electrode is in a second position in contactwith tissue along the inner circumference different from the firstposition, and the tip electrode is used to ablate tissue at the secondposition. This procedure can be repeated to form a lesion of the desiredlength along the inner circumference. This design permits the user tohave more control when ablating about a circumference of a tubularregion in or around the heart, e.g., a pulmonary vein, the coronarysinus, the superior vena cava, or the pulmonary outflow tract.

DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of an embodiment of the catheter of theinvention;

FIG. 2 is a side cross-sectional view of a catheter body according tothe invention, including the junction between the catheter body and theintermediate section;

FIG. 3 is a side cross-sectional view of the intermediate section,including the junction between the intermediate section and the ablationassembly;

FIG. 4 is a schematic perspective view of an ablation assembly accordingto the invention;

FIG. 5 is a schematic perspective view of an alternative ablationassembly according to the invention;

FIG. 6 is a side view of the ablation assembly of FIG. 5;

FIG. 7 is a side cross-sectional view of the distal end of an ablationassembly according to the invention; and

FIG. 8 is a perspective view of an alternative tip electrode accordingto the invention.

DETAILED DESCRIPTION

In a particularly preferred embodiment of the invention, there isprovided a catheter having an ablation assembly at its distal end. Asshown in FIG. 1, the catheter comprises an elongated catheter body 12having proximal and distal ends, an intermediate section 14 at thedistal end of the catheter body, a control handle 16 at the proximal endof the catheter body, and an ablation assembly 17 mounted at the distalend of the catheter to the intermediate section.

With reference to FIG. 2, the catheter body 12 comprises an elongatedtubular construction having a single, axial or central lumen 18. Thecatheter body 12 is flexible, i.e. bendable, but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 20 made of polyurethaneor PEBAX. The outer wall 20 comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 12 so that, when the control handle 16 is rotated, theintermediate section 14 of the catheter 10 will rotate in acorresponding manner.

The outer diameter of the catheter body 12 is not critical, but ispreferably no more than about 8 french, more preferably about 7 french.Likewise, the thickness of the outer wall 20 is not critical, but isthin enough so that the central lumen 18 can accommodate a puller wire,one or more lead wires, and any other desired wires, cables or tubes. Ifdesired the inner surface of the outer wall 20 is lined with astiffening tube (not shown) to provide improved torsional stability. Aparticularly preferred catheter has an outer wall 20 with an outerdiameter of from about 0.090 inch to about 0.94 inch and an innerdiameter of from about 0.061 inch to about 0.065 inch.

The intermediate section 14 comprises a short section of tubing 22having three lumens. The first lumen 30 carries one or more lead wires50 or other wires discussed further below, the second lumen 32 carries apuller wire 64, and the third lumen 34 carries a support member 24. Thetubing 22 is made of a suitable non-toxic material that is preferablymore flexible than the catheter body 12. A presently preferred materialfor the tubing 22 is braided polyurethane, i.e. polyurethane with anembedded mesh of braided stainless steel or the like. The size of eachlumen is not critical, but is sufficient to house the lead wires, pullerwire or support member.

The useful length of the catheter, i.e. that portion that can beinserted into the body excluding the ablation assembly 17, can vary asdesired. Preferably, the useful length ranges from about 110 cm to about120 cm. The length of the intermediate section 14 is a relatively smallportion of the useful length, and preferably ranges from about 3.5 cm toabout 10 cm, more preferably from about 5 cm to about 6.5 cm.

A preferred means for attaching the catheter body 12 to the intermediatesection 14 is illustrated in FIG. 2. The proximal end of theintermediate section 14 comprises an outer circumferential notch 26 thatreceives the inner surface of the outer wall 22 of the catheter body 12.The intermediate section 14 and catheter body 12 are attached by glue orthe like.

If desired, a spacer (not shown) can be located within the catheter bodybetween the distal end of the stiffening tube (if provided) and theproximal end of the intermediate section. The spacer provides atransition in flexibility at the junction of the catheter body andintermediate section, which allows this junction to bend smoothlywithout folding or kinking. A catheter having such a spacer is describedin U.S. Pat. No. 5,964,757, the disclosure of which is incorporatedherein by reference.

At the distal end of the intermediate section 14 is the ablationassembly 17, as shown in FIGS. 3 to 7. In the depicted embodiment, theablation assembly 17 comprises the distal end of the support member 24covered by a non-conductive covering 28. In the embodiment of FIG. 4,the ablation assembly 17 comprises a generally straight proximal region38 and a generally circular main region 39 that is generally transverseto the catheter body. The proximal region 38 is mounted on theintermediate section 14, as described in more detail below, so that itsaxis is generally parallel to the axis of the intermediate section. Inthis embodiment, the proximal region 38 is generally at the center ofthe generally circular main region 39. The proximal region 38 preferablyhas an exposed length, i.e. not contained within the intermediatesection 14, ranging from about 3 mm to about 12 mm, more preferablyabout 3 mm to about 8 mm, still more preferably about 5 mm, but can varyas desired.

The generally circular main region 39 does not have to form a completecircle, but should be at least about 180°, e.g. a semi-circle, morepreferably at least about 270°, still more preferably at least about320°. In the preferred embodiment, the generally circular main region 39forms at least a complete circle, e.g. is at least 360°. If desired, thegenerally circular main region can comprise more than one loop orcircle, so that it has, for example, a spiral or conical shape. Thegenerally circular main region 39 is generally transverse to thecatheter body 12 and intermediate section 14, and preferably forms anangle with the catheter body ranging from about 80° to about 100°, morepreferably about 90°. The generally circular main region 39 has an outerdiameter preferably ranging from about 2 mm to about 40 mm, morepreferably from about 10 mm to about 25 mm, still more preferably fromabout 12 mm to about 20 mm, even more preferably about 15 mm.

In an alternative embodiment, as shown in FIGS. 5 and 6, the ablationassembly 17 further comprises a generally straight distal region 40 thatextends substantially tangentially from the generally circular mainregion 39, as shown in FIG. 5. In this embodiment, the proximal region38 is at the side of the generally circular main region 39, as bestshown in FIG. 6.

The support member 24 is made of a material having shape-memory, i.e.that can be straightened or bent out of its original shape upon exertionof a force and is capable of substantially returning to its originalshape upon removal of the force. A particularly preferred material forthe support member is a nickel/titanium alloy. Such alloys typicallycomprise about 55% nickel and 45% titanium, but may comprise from about54% to about 57% nickel with the balance being titanium. A preferrednickel/titanium alloy is nitinol, which has excellent shape memory,together with ductility, strength, corrosion resistance, electricalresistivity and temperature stability. The non-conductive covering 28can be made of any suitable material, and is preferably made of abiocompatible plastic such as polyurethane or PEBAX. If desired, thesupport member 24 can be eliminated and the distal end of thenon-conductive covering 28 can be pre-formed to have the desired curveof the ablation assembly.

A tip electrode 35 is mounted at the distal end of the ablation assembly17 for ablating tissue. As shown in FIG. 7, the tip electrode 35 has anexposed region 35 a and a stem 35 b that extends into the non-conductivecovering 28. In the embodiment of FIG. 7, the tip electrode 35 has agenerally cylindrical exposed region 35 a with an outer diameterapproximately the same as the outer diameter of the non-conductivecovering 28 by polyurethane glue or the like.

In an alternative embodiment, as shown in FIG. 8, the exposed region 35a of the tip electrode has a bulb shape with a varying outer diameterwherein at least a portion of the exposed region extends beyond theouter circumference of the non-conductive covering 28. It has been foundthat a catheter having a bulb-shaped tip electrode can provide bettercontact with the tissue based on the outward spring-like force exertedby the generally circular ablation assembly. Other tip electrode shapeswill be apparent to one skilled in the art. For example, an asymmetricaltip electrode (not shown) could be provided where the side of theelectrode that would be in contact with the tissue, i.e. on the outsideof the ablation assembly, extends beyond the outer wall of thenon-conductive covering 28 and the inner side of the tip electrode isgenerally even with the wall of the non-conductive covering.

An electrode lead wire 50 connects the tip electrode 35 to a suitablesource of ablation energy (not shown), preferably radio frequency (RF)energy. The distal end of the lead wire 50 is soldered in a first blindhole 51 in the proximal end of the tip electrode 35. The lead wire 50extends between the non-conductive covering 28 and the support member24. The proximal end of the lead wire 50 is electrically connected to asuitable connector 37, which is connected to the source of ablationenergy as is known in the art. The lead wire 50 extends through thefirst lumen 30 of the intermediate section 14, the central lumen 18 ofthe catheter body 12, and the control handle 16, and terminates at itsproximal end in the connector 37. In the depicted embodiment, theportion of the lead wire 50 extending through the central lumen 18 ofthe catheter body 12, control handle 16 and proximal end of theintermediate section 14 is enclosed within a protective sheath 62 toprevent contact with other components within the lumen of the catheterbody and in the handle. The protective sheath 62 can be made of anysuitable material, preferably polyimide. The protective sheath 62 isanchored at its distal end to the proximal end of the intermediatesection 14 by gluing it in the first lumen 30 with polyurethane glue orthe like. As would be recognized by one skilled in the art, theprotective sheath can be eliminated if desired.

A temperature sensor is provided for monitoring the temperature of thetip electrode 35. Any conventional temperature sensor, e.g. athermocouple or thermistor, may be used. In the embodiment shown in FIG.7, the temperature sensor comprises a thermocouple formed by an enameledwire pair. One wire of the wire pair is a copper wire 53, e.g. a number40 copper wire. The other wire of the wire pair is a constantan wire 54.The wire 53 and 54 of the wire pair are electrically isolated from eachother except at their distal ends where they are twisted together,covered with a short piece of plastic tubing 55, e.g. polyimide, andcovered with epoxy. The plastic tubing 55 is then attached in a secondblind hole 56 of the tip electrode 35, by polyurethane glue or the like.Alternatively, the wires 53 and 54 can be soldered into the second blindhole 56 or otherwise attached to the tip electrode 35. The wires 53 and54 extend through the first lumen 30 in the intermediate section 14 andthrough the central lumen 18 of the catheter body 12 along with the leadwire 50. The wires 53 and 54 then extend out through the control handle16 and to a connector (not shown) connectable to a temperature monitor(not shown). Preferably, the wires 53 and 54 extend through theprotective sheath 62 in the catheter body 12.

Additionally, a safety wire 57 is provided to further secure the tipelectrode 35 to the ablation assembly 17 and assure that the tipelectrode does not fall off in the patient's body. The safety wire ispreferably a metal wire having its distal end soldered in a third blindhole 58 in the tip electrode 35 and its proximal end soldered orotherwise attached in the control handle 126. In the depictedembodiment, the safety wire 57 extends through the first lumen 30 in theintermediate section 14 and through the central lumen 18 of the catheterbody 12 along with the lead wires 50 and thermocouple wires 53 and 54.Other arrangements for attaching the safety wire can be provided, aswould be recognized by one skilled in the art, or the safety wire can beeliminated.

If desired, one or more ring electrodes (not shown) can be mounted onthe non-conductive covering 28 of the generally circular main region 39of the ablation assembly 17. Such ring electrodes might be desirable,for example, for mapping the region to be ablated before ablation beginsor after ablation to assure that the lesions blocked the electricalactivity as desired. A description of a catheter including such ringelectrodes is described in U.S. patent application Ser. No. 09/551,467,entitled “Catheter Having Mapping Assembly,” the entire disclosure ofwhich is incorporated herein by reference. If desired, additional ringelectrodes (not shown) could be mounted elsewhere along the ablationassembly 17 and/or intermediate section 14.

The junction of the intermediate section 14 and ablation assembly 17 isshown in FIG. 3. The non-conductive covering 28 is attached to thetubing 22 of the intermediate section by glue or the like. The supportmember 24 extends from the third lumen 34 into the non-conductivecovering 28. The proximal end of the support member 24 terminates ashort distance within the third lumen 34, approximately 5 mm, so as notto adversely affect the ability of the intermediate section 14 todeflect. However, if desired, the proximal end of the support member 24can extend into the catheter body 12.

The lead wires 50, thermocouple wires 53 and 54 and safety wire 57extend through the first lumen 30 of the intermediate section 14,through the central lumen 18 of the catheter body 12, and the controlhandle 16, and terminate at their proximal end in the connector 37. Asnoted above, the portion of the wires extending through the centrallumen 18 of the catheter body 12, control handle 16 and proximal end ofthe intermediate section 14 are enclosed within a protective sheath 62,which can be made of any suitable material, preferably polyimide. Theprotective sheath 62 is anchored at its distal end to the proximal endof the intermediate section 14 by gluing it in the first lumen 30 withpolyurethane glue or the like.

The puller wire 64 is provided for deflection of the intermediatesection 14. The puller wire 64 extends through the catheter body 12, isanchored at its proximal end to the control handle 16, and is anchoredat its distal end to the intermediate section 14. The puller wire 64 ismade of any suitable metal, such as stainless steel or Nitinol, and ispreferably coated with Teflon® or the like. The coating impartslubricity to the puller wire 64. The puller wire 64 preferably has adiameter ranging from about 0.006 to about 0.010 inch.

A compression coil 66 is situated within the catheter body 12 insurrounding relation to the puller wire 64, as shown in FIG. 2. Thecompression coil 66 extends from the proximal end of the catheter body12 to the proximal end of the intermediate section 14. The compressioncoil 66 is made of any suitable metal, preferably stainless steel. Thecompression coil 66 is tightly wound on itself to provide flexibility,i.e. bending, but to resist compression. The inner diameter of thecompression coil 66 is preferably slightly larger than the diameter ofthe puller wire 64. The Teflon® coating on the puller wire 64 allows itto slide freely within the compression coil 66. The outer surface of thecompression coil is covered by a flexible, non-conductive sheath 58,e.g. made of polyimide tubing.

The compression coil 66 is anchored at its proximal end to the outerwall 20 of the catheter body 12 by proximal glue joint 70 and at itsdistal end to the intermediate section 14 by distal glue joint 72. Bothglue joints 70 and 72 preferably comprise polyurethane glue or the like.The glue may be applied by means of a syringe or the like through a holemade between the outer surface of the catheter body 12 and the centrallumen 18. Such a hole may be formed, for example, by a needle or thelike that punctures the outer wall 20 of the catheter body 12 which isheated sufficiently to form a permanent hole. The glue is thenintroduced through the hole to the outer surface of the compression coil66 and wicks around the outer circumference to form a glue joint aboutthe entire circumference of the compression coil.

The puller wire 64 extends into the second lumen 32 of the intermediatesection 14. Preferably, the puller wire 64 is anchored at its distal endto the distal end of the intermediate section 14, as shown in FIG. 3.Specifically, a T-shaped anchor is formed, which comprises a short pieceof tubular stainless steel 80, e.g. hypodermic stock, which is fittedover the distal end of the puller wire 64 and crimped to fixedly secureit to the puller wire. The distal end of the tubular stainless steel 80is fixedly attached, e.g. by welding, to a cross-piece 82 formed ofstainless steel ribbon or the like. The cross-piece 82 sits beyond thedistal end of the second lumen 32. The cross-piece 82 is larger than thelumen opening and, therefore, cannot be pulled through the opening. Thedistal end of the second lumen 32 is then filled with glue or the like,preferably polyurethane glue. Within the second lumen 32 of theintermediate section 14, the puller wire 64 extends through a plastic,preferably Teflon®, puller wire sheath (not shown), which prevents thepuller wire 64 from cutting into the wall of the intermediate section 14when the intermediate section is deflected.

Longitudinal movement of the puller wire 64 relative to the catheterbody 12, which results in deflection of the intermediate section 14, isaccomplished by suitable manipulation of the control handle 16. Examplesof suitable control handles for use in the present invention aredisclosed, for example, in U.S. Pat. Nos. Re 34,502 and 5,897,529, theentire disclosures of which are incorporated herein by reference.

In use, a suitable guiding sheath is inserted into the patient with itsdistal end positioned at a desired mapping location. An example of asuitable guiding sheath for use in connection with the present inventionis the Preface™ Braided Guiding Sheath, commercially available fromBiosense Webster, Inc. (Diamond Bar, Calif.). The distal end of thesheath is guided into one of the atria. A catheter in accordance withthe present invention is fed through the guiding sheath until its distalend extends out of the distal end of the guiding sheath. As the catheteris fed through the guiding sheath, the ablation assembly 17 isstraightened to fit through the sheath. Once the distal end of thecatheter is positioned at the desired mapping location, the guidingsheath is pulled proximally, allowing the deflectable intermediatesection 14 and ablation assembly 17 to extend outside the sheath, andthe ablation assembly 17 returns to its original shape. The ablationassembly 17 is then inserted into a pulmonary vein or other tubularregion (such as the coronary sinus, superior vena cava, or inferior venacava) so that the outer circumference of the generally circular mainregion 39 of the assembly is in contact with a circumference inside thetubular region and the tip electrode 35 is generally in contact with thetissue.

The circular arrangement of the ablation assembly 17 provides a stablemechanism for keeping the tip electrode 35 in a desired location forablation. To ablate a circumferential lesion in the tubular region, theuser rotates the ablation assembly 17 by rotating the control handle 16and applies ablation energy through the tip electrode 35 at adjacentpoints along the circumference. The design of the ablation assemblypermits the user to more easily ablate about a circumference compared tousing a tip electrode on a straight catheter, where it is more difficultto accurately move the tip electrode about the circumference of thetubular region.

As will be recognized by one skilled in the art, it is easier to turnthe ablation assembly in a direction such that the tip electrode isbeing pulled rather than pushed. For example, in the embodimentsdepicted in FIGS. 4 and 5, where the ablation assemblies are formed in aclockwise direction, it is preferable to turn the assemblies in acounterclockwise direction. Accordingly, if desired, an arrow or otherindicator (not shown) can be included on the handle or proximal end ofthe catheter body to indicate to the user the preferred direction forrotating the ablation assembly in the body.

If desired, two or more puller wires can be provided to enhance theability to manipulate the intermediate section. In such an embodiment, asecond puller wire and a surrounding second compression coil extendthrough the catheter body and into an additional off-axis lumen in theintermediate section. The first puller wire is preferably anchoredproximal to the anchor location of the second puller wire. Suitabledesigns of catheters having two or more puller wires, including suitablecontrol handles for such embodiments, are described, for example, inU.S. Pat. Nos. 6,123,699, 6,171,277, 6,183,435, 6,183,463, 6,198,974,6,210,407, and 6,267,746, the disclosures of which are incorporatedherein by reference.

Alternatively, a second puller wire (not shown) can be included to alterthe diameter of the distal end of the ablation assembly. Such anarrangement is generally described in U.S. Pat. No. 5,626,136, thedisclosure of which is incorporated herein by reference. Theabove-referenced control handles could be used to manipulate the secondpuller wire.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest andfairest scope.

1. A method for ablating tissue within a tubular region of or near the heart having an inner circumference, the method comprising: inserting into the tubular region an ablation assembly at a distal end of a catheter, the catheter comprising an elongated tubular catheter body having proximal and distal ends, an axis, and at least one lumen extending therethrough, and wherein the ablation assembly has a preformed generally circular curve having an outer circumference and being generally transverse to the axis of the catheter body, the ablation assembly further comprising a generally straight distal region extending beyond the generally circular curve and substantially tangentially from the generally circular curve, wherein the ablation assembly comprises a generally circularly curved flexible tubing having proximal and distal ends, the flexible tubing carrying a generally bulb-shaped tip electrode at its distal end; contacting the inner circumference of the tubular region with at least a portion of the outer circumference of the generally circular curve so that the tip electrode is in a first position in contact with tissue along the inner circumference of the tubular region; ablating the tissue along the inner circumference of the tubular region at the first position with the tip electrode; rotating the catheter so that the tip electrode is in a second position in contact with other tissue along the inner circumference of the tubular region; and ablating the other tissue at the second position with the tip electrode.
 2. A method according to claim 1, wherein the tubular region is selected from the group consisting of pulmonary veins, the coronary sinus, the superior vena cava, and the inferior vena cava.
 3. A method according to claim 1, wherein the tubular region is the pulmonary vein.
 4. A method according to claim 1, wherein the tip electrode has an exposed region that is generally cylindrical.
 5. A method according to claim 1, wherein the tip electrode has an exposed region, at least a portion of which has an outer diameter greater than the outer diameter of the flexible tubing of the ablation assembly.
 6. A method according to claim 1, wherein the generally circular curve has an outer diameter ranging from about 10 mm to about 25 mm.
 7. A method according to claim 1, wherein the generally circular curve has an outer diameter ranging from about 12 mm to about 20 mm.
 8. A method according to claim 1, wherein the generally circular curve is at least about 320°.
 9. A method according to claim 1, wherein the generally circular curve is at least about 360°.
 10. A method according to claim 1, wherein the generally circular curve consists of a single generally circular curve.
 11. A method according to claim 1, wherein the ablation assembly further comprises a support member comprising a material having shape memory extending through at least a portion of the flexible tubing.
 12. A method according to claim 1, further comprising an intermediate section disposed between the catheter body and the ablation assembly, the intermediate section having at least one lumen extending therethrough and being more flexible than the catheter body.
 13. A method for ablating tissue within a tubular region of or near the heart having an inner circumference, the method comprising: inserting into the tubular region an ablation assembly at a distal end of a catheter, the catheter comprising an elongated tubular catheter body having proximal and distal ends, an axis, and at least one lumen extending therethrough, and wherein the ablation assembly has a preformed generally circular curve having an outer circumference and being generally transverse to the axis of the catheter body, the ablation assembly further comprising a generally straight distal region extending beyond the generally circular curve and substantially tangentially from the generally circular curve, wherein the ablation assembly comprises a generally circularly curved flexible tubing having proximal and distal ends, the flexible tubing carrying a generally bulb-shaped tip electrode at its distal end, wherein the tip electrode has an exposed region, at least a portion of which has an outer diameter greater than the outer diameter of the flexible tubing of the ablation assembly; contacting the inner circumference of the tubular region with at least a portion of the outer circumference of the generally circular curve so that the tip electrode is in a first position in contact with the tissue along the inner circumference of the tubular region; and ablating the tissue along the inner circumference of the tubular region at the first position with the tip electrode.
 14. A method according to claim 13, wherein the tubular region is selected from the group consisting of pulmonary veins, the coronary sinus, the superior vena cava, and the inferior vena cava.
 15. A method according to claim 13, wherein the tubular region is a pulmonary vein.
 16. A method according to claim 13, wherein the tip electrode has an exposed region that is generally cylindrical.
 17. A method according to claim 13, wherein the generally circular curve has an outer diameter ranging from about 10 mm to about 25 mm.
 18. A method according to claim 13, wherein the generally circular curve has an outer diameter ranging from about 12 mm to about 20 mm.
 19. A method according to claim 13, wherein the generally circular curve is at least about 320°.
 20. A method according to claim 13, wherein the generally circular curve is at least 360°.
 21. A method according to claim 13, wherein the generally circular curve consists of a single generally circular curve.
 22. A method for ablating tissue within a tubular region of or near the heart having an inner circumference, the method comprising: inserting into the tubular region an ablation assembly at a distal end of a catheter, the catheter comprising an elongated tubular catheter body having proximal and distal ends, an axis, and at least one lumen extending therethrough, and wherein the ablation assembly has a preformed generally circular curve having an outer circumference and being generally transverse to the axis of the catheter body, the ablation assembly further comprising a generally straight distal region extending beyond the generally circular curve and substantially tangentially from the generally circular curve, wherein the ablation assembly comprises a generally circularly curved flexible tubing having proximal and distal ends, the flexible tubing carrying a generally bulb-shaped tip electrode at its distal end; contacting the inner circumference of the tubular region with at least a portion of the outer circumference of the generally circular curve so that the tip electrode is in a first position in contact with tissue along the inner circumference of the tubular region; ablating the tissue along the inner circumference of the tubular region at the first position with the tip electrode; rotating the catheter so that the tip electrode is in a second position in contact with other tissue along the inner circumference of the tubular region, wherein the ablation assembly is rotated in a direction such that the tip electrode is pulled rather than pushed into the rotation; and ablating the other tissue at the second position with the tip electrode.
 23. A method for ablating tissue within a tubular region of or near the heart having an inner circumference, the method comprising: inserting into the tubular region an ablation assembly at a distal end of a catheter, the catheter comprising an elongated tubular catheter body having proximal and distal ends, an axis, and at least one lumen extending therethrough, and wherein the ablation assembly has a main region having a preformed generally circular curve having an outer circumference and being generally transverse to the axis of the catheter body, the ablation assembly also having a generally straight distal region extending beyond the generally circular curve of the main region and substantially tangentially to the generally circular curve of the main region, the ablation assembly comprising a generally circularly curved flexible tubing having proximal and distal ends, the flexible tubing carrying a generally bulb-shaped tip electrode at its distal end; contacting the inner circumference of the tubular region with at least a portion of the outer circumference of the generally circular curve so that the tip electrode is in a first position in contact with tissue along the inner circumference of the tubular region; ablating the tissue along the inner circumference of the tubular region at the first position with the tip electrode.
 24. The method according to claim 23, further comprising: rotating the catheter so that the tip electrode is in a second position in contact with other tissue along the inner circumference of the tubular region; and ablating the other tissue at the second position with the tip electrode.
 25. The method according to claim 24, wherein the ablation assembly is rotated in a direction such that the tip electrode is pulled rather than pushed into the rotation.
 26. A method for ablating tissue within a tubular region of or near the heart having an inner circumference, the method comprising: inserting into the tubular region an ablation assembly at a distal end of a catheter, the catheter comprising an elongated tubular catheter body having proximal and distal ends, an axis, and at least one lumen extending therethrough, and wherein the ablation assembly has a preformed generally circular curve having an outer circumference and being generally transverse to the axis of the catheter body, the ablation assembly comprising a generally straight distal region extending beyond the generally circular curve and substantially tangentially from the generally circular curve, the ablation assembly comprising a generally circularly curved flexible tubing having proximal and distal ends, the flexible tubing carrying a generally bulb-shaped tip electrode at its distal end, the catheter further comprising a safety wire for securing the tip electrode to the ablation assembly, the safety wire having a distal end attached in the tip electrode; contacting the inner circumference of the tubular region with at least a portion of the outer circumference of the generally circular curve so that the tip electrode is in a first position in contact with tissue along the inner circumference of the tubular region; and ablating the tissue along the inner circumference of the tubular region at the first position with the tip electrode.
 27. The method according to claim 26, further comprising: rotating the catheter so that the tip electrode is in a second position in contact with other tissue along the inner circumference of the tubular region; and ablating the other tissue at the second position with the tip electrode. 